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Show 32 JJARWINIANA. Some suppose that . rac~s cannot be perpetuated indefinitely evtm by keeping up the conditions under which they were fixed; but the high antiquity of several, and the actual fixity of many of them, negative this . assumption. " To assert that .we could not breed our cart and race horses, long and short horned cattle, and poultry of various breeds, for almost an infinite number of generations, would be opposed to all experience." Why variet.ies develop so readily and deviate so widely under domestication, while they are apparently so rare or so transient in free Nature, may easily . be shown. In Nature, even with hermaphrodite plants, _ there is a vast amount of cross-fertilization among various individuals of the same species. The inevitable result of this (as was long ago explained in this J ournal 1 ) is to repress variation, to keep the mass of a species comparatively homogeneous over any area in which it abounds in individuals. Starting from a suggestion of the late Mr. Knight, now so familiar, that close interbreeding diminishes vigor and fertility; 2 and perceiving that bisexuality is ever aimed at in Nature-being attained physiologically in numerous cases where it is not structurally-Yr. Darwin has worked out the subject in detail, and shown haw general is the concurrence, either habitual or occasional, of two hermaphrodite individuals in the reproduction of their kind; and has drawn the philosophical infer-t Volume xvii. (2), 1854, p. 13. ~ We suspect that this is not an ultimate fact, but a natural conse· quence of inheritance-the inheritance of disease or of tendency to disease, which close interbreeding perpetuates and accumulates, but wide breeding may neutralize or eliminate. THE ORIGIN OF SPECIES. 33 ence that probably no organic being self-fertilizes indefinitely; but that a cross with another individual is occasionally-perhaps at very long intervals-indispensable. We refer the reader to the section on the· intercrossing of individuals (pp. 96-101), and also to an article in the Gardeners' Chronicle a year and a half ago, for the details of a very interesting contribution to science, irrespective of theory. - In domestication, this intercrossing may be prevented; and in this prevention lies the art of producing varieties. But "the art itself is Nature," f;ince the whole art consists in allowing the most universal of all natural tendencies in organic things (inheritance) to operate uncontrolled by other and obviously incidental tendencies. No ne·1V power, no artificial force, is brought into play either by separating the stock of a desirable variety so as to prevynt mixture, or by selecting for breeders those individuals which most largely partake of the pecularities for which the breed is valued.1 We see everywhere around us the remarkable results which. Nature may be said to have brought about under artificial selection and separation. Could she accomplish similar results when left to herself 1 Variations might beg~n, we know .they do begin, in a wild state. But would any of them be preserved and carried to an equal degree of deviation? Is there anything inN ature which in the long-run may answer to 1 The rules and processes of Qrecders of animals, and their results, are so familiar that they need not be particularized. Less is popularly known about the production of vegetable races. We refer our readers back to this Journal, vol. xxvii., pp. 440-442 (May, 1859), for an abstract of the papers of M. Vilmorin upon this subject. |
